1. Field
The embodiments relate to cooling by removing heat, and more particularly to removing heat of a device using forced convection liquid metal combined with thermoelectric and a ferrofluid.
2. Description of the Related Art
Cooling is one of the main concerns for computer and processor manufacturers and developers. The industry depends on functional cooling techniques to help cool their rapidly advancing chips, which tend to run hotter and hotter. Without proper cooling, design engineers will end up sacrificing performance and power for lower temperatures and stability.
Initially, passive cooling was enough to keep central processing units (CPUs) in a stable state. As chips evolved, however, so did cooling due to necessity. A transition from aluminum and copper to graphite heat sinks, and from passive to active cooling (i.e., using a fan to force out the heat that dissipates into the CPUs surrounding airflow) has kept pace with the advances in processing power. Some computer designers have used water-cooling, which uses water to transfer the heat directly from a chip's surface more efficiently and effectively. Water-cooling, however, is not enough to completely eliminate certain hot areas that form on processors with higher heat output.
One newer technique uses active microchannel cooling, which actively cools a processor with micro channels. Microchannels are extremely small grooves and ridges machined into the silicon block that collect heat from the processor. The microchannels are about the width of a human hair, less than 1/32 of an inch wide. As compared with water-cooling, the microchannels in the active microchannel cooling system are much more efficient, since there is a larger surface area for the heat to dissipate. Another advantage of microchannels is that since they are machined using standard silicon machining techniques, the price of manufacturing is low and any defects in the product are minimal. One of the benefits of using microchannels for cooling is the efficient heat removal from CPU hot spots. Typical microchannels are approximately 1.5 mm away from any given hot area. Therefore, the distance that the heat must travel to be dissipated is effectively reduced. An interesting aspect of active microchannel cooling is that the microchannels are made from silicon, a material not usually known for its heat-dissipation properties. Since silicon is a semiconductor, it shares some characteristics of metals and non-metals. Metals are usually good conductors of heat, but compared to metals, silicon dissipates heat poorly. Advantages of using silicon are, for example, silicon is the second most abundant element in the earth's crust. Therefore, cooling via microchannels help keep the price of computers/processors down.
An electro-kinetic pump is a feature of active microchannel cooling. The pump uses an electro-kinetic effect to propel cooling fluid through a porous glass disk without any moving parts. The pump works by positively charging the cooling fluid, therefore generating positively charged hydrogen atoms. The hydrogen atoms then repel against the negatively charged glass and push the fluid through the disk. Because it uses no moving parts, the pump should be reliable and is almost completely silent.
Besides microchannel cooling using a silent pump, an optional fan can be attached to a radiator. The radiator in the active microchannel cooling system doesn't need to have a fan attached, and the system is completely silent unless the user opts to have maximum cooling. A small, yet important factor in cooling is the size of any cooling system. While air-cooling requires large fans, active microchannel cooling uses a thin silicon block and a small radiator. Compared to water-cooling systems, the size of the active microchannel cooling is very small.
One drawback to active microchannel cooling is the installation process. As compared to adding an air-cooling system to a computer, which is as simple as screwing a heat sink to the motherboard and attaching a fan, active microchannel cooling can require installing brackets for the pump and radiator, and installing tubing in a computer system.
Another type of cooling technique is the use of a heat pipe. A heat pipe is self-powered and transfers heat to a side edge of a computer or notebook computer, where air fins or a tiny fan can be used to dissipate the unwanted heat into air. A heat pipe uses tiny liquid-filled pipes to shuttle heat to pre-chosen locations for dispersal. In the heat pipe loop, heat from a processor changes liquid, for example methanol, to vapor. The vapor absorbs heat at a pre-selected site, changes back to liquid and wicks back to its starting point to collect more heat.
Thermoelectric modules (TEM) have also been used as active cooling devices. By placing a TEM between a device or object to be cooled, such as an integrated circuit, and a heat sink and supplying the TEM with a current, the TEM transfers heat from the integrated circuit to the heat sink. The phenomenon is called the Peltier effect. The TEM consists of ceramic plates with p-type semiconductor material and n-type semiconductor material between the plates. The elements of semiconductor material are connected electrically in series. When a direct current (DC) voltage is applied to the semiconductor material, electrons pass from the p-type material to the n-type material. The elements are arranged in a manner such that when a DC voltage is applied, heat is transferred from one side of the TEM to the other. The rate of transfer is proportional to the current and the number of p-n junctions.
The problem of cooling computers, notebooks and processors will continue as performance increases.